1. Field of the Invention
The invention relates to the reduction of the peak-to-mean average amplitude in a signal transmitted in a power amplifier, and particularly but not exclusively to such reduction in the power amplifier of a multicarrier communication system utilizing an EDGE clipper.
2. Description of the Related Art
Mobile communication systems, such as enhanced data rates for GSM (Global System for Mobile communications) evolution (EDGE) systems, utilize a power amplifier in a transmitter at the base transceiver station for transmitting signals.
It is known that a signal with a high peak-to-mean (average) ratio (PAR) sets high requirements for power amplifier linearity, and therefore reduces achievable power efficiency and increases the power consumption of the power amplifier. In order to improve efficiency, algorithms are utilized to reduce the peak-to-mean ratio of a transmitted EDGE signal. Nevertheless, system requirements set limits for achievable PAR reduction. The main transmission requirements are the signal frequency, peak EVM (Error Vector Magnitude) amplitude, and RMS (Root Mean Square) EVM.
Clipping algorithms provide one method to reduce the PAR, but at the cost of increasing the EVM of the transmitted signal. Different clipping algorithms have been previously studied in the case of WCDMA (Wideband Code Division Multiple Access) signals, and as a result some algorithms have been proposed for implementation. In the case of multicarrier EDGE signaling, the topic of clipping has been specifically studied.
The challenge is to minimize the PAR, but preferably without compromising the frequency requirement, the peak EVM requirement, and the RMS EVM requirement of the transmitted signal.
There has been ongoing discussion about different methods to minimize peak-to-average ratio (PAR) in EDGE transmissions. Minimizing PAR in EDGE enhances the achievable efficiency of the power amplifier. However in known suggested solutions the time-domain properties of the PAR reduced signal can be quite rapidly deteriorated.